Polymerization process

ABSTRACT

Polymerization processes for ethylene and at least one mono-1-olefin comonomer having from about three to eight carbon atoms per molecule in the presence of a twice-aged catalyst system comprising chromium supported on a silica-titania support and a trialkylboron compound is provided. Novel ethylene copolymers also are produced.

BACKGROUND OF THE INVENTION

This invention relates to the polymerization and copolymerization of amono-1-olefin monomer, such as ethylene, with a higher alpha-olefincomonomer.

Supported chromium catalysts long have been a dominant factor in theproduction of high density olefin polymers, such as polyethylene. Asoriginally commercialized, these catalyst systems were used in solutionpolymerization processes. However, it became evident early that a slurryprocess was a more economical route to many commercial grades of olefinpolymers, that is, a polymerization process carried out at a temperaturelow enough that the resulting polymer is largely insoluble in thediluent.

It is well known that mono-1-olefins, such as ethylene, can bepolymerized with catalyst systems employing vanadium, chromium or othermetals on a support, such as alumina, silica, aluminum phosphate,titania, zirconium, magnesium and other refractory metal supports.Initially, such catalyst systems primarily were used to formhomopolymers of ethylene. Soon copolymers were developed whereincomonomers such as propylene, 1-butene, 1-hexene or other highermono-1-olefins were copolymerized with ethylene to provide resinstailored to specific end uses.

Often, high density and/or high molecular weight copolymers can be usedfor blow molding applications because the blow molding process enablesrapid processing into a desired molded product. Theoretically, any typeof resin can be made to flow more easily by merely lowering themolecular weight, (i.e., by raising the melt index.) However, this israrely practical because of other penalties that occur because of ahigher melt index (MI). A higher melt index can result in a decrease inmelt strength, which can cause a parison to tear or sag during extrusionbecause the parison is unable to resist its own weight. As used in thisdisclosure, a parison is an extruded cylinder of molten polymer beforeit is blown by air pressure to fill a mold. Additionally, a higher MIcan cause bottle properties such as environmental stress crackresistance (ESCR) and impact strength to decrease. One of the mostprevalent problems associated with raising the MI is an increase of theamount of swell exhibited by the resin as it exits the die.

Two kinds of swell are critical during blow molding. These are “weightswell” and “diameter swell”; the later also is referred to herein as“die swell”. As polymer, or resin, is extruded under pressure through adie opening and into a mold, a polymer has a tendency to swell as itexits the die. This is known as weight swell and is determinative of thethickness of bottle wall, as well as the overall weight of the resultantblow molded product. For example, a resin which is extruded through a0.02 inch die gap might yield a bottle wall thickness of 0.06 inches, inwhich case the weight swell is said to be 300%. A resin that swells toomuch can produce a bottle with too thick of a wall. To compensate, thedie opening or gap can be narrowed by manual adjustment. However, anydecrease in die gap can increase the resistance to the flow of the resinthrough the die. Narrower die gaps can result in higher shear ratesduring extrusion which also can increase in melt fracture leading to arough bottle surface. Thus, a resin which can be described as easilyprocessable must exhibit low weight swell, which allows a wide die gap.

Diameter, or die, swell refers to how much the parison flares out as itis extruded from the die. For example, a resin extruded through acircular die of one (1) inch diameter can yield a parison tube of 1.5inches in diameter; the die swell is said to be 50%. Die swell issignificant because molds usually are designed for a certain amount offlare; too much die swell can interfere with molding of a bottle handle.A high degree of weight swell often causes high die swell because of thenarrow gap that accompanies it. Unfortunately, increasing the melt indexof a resin usually increases both weight swell and die swell of thepolymer. Thus, as used herein, a resin which is considered easilyprocessable also should exhibit low die swell.

SUMMARY OF THE INVENTION

Therefore, it is an object of this invention to provide an improvedolefin polymerization process.

It is another object of this invention to provide a process to producecopolymers of ethylene and mono-1-olefins that can be processed atincreased production rates and have a decreased weight swell.

It is still another object of this invention to provide a process toproduce copolymers of ethylene and mono-1-olefins that can be processedat increased production rates and have a decreased die swell.

In accordance with this invention, herein is provided a polymerizationprocess comprising contacting under slurry polymerization conditions ata temperature within a range of about 200° F. to about 226° F. (about93° C. to about 108° C.) in an isobutane diluent:

a) ethylene monomer;

b) at least 1 mono-1-olefin comonomer having about three to eight carbonatoms per molecule;

c) a catalyst system comprising chromium supported on a silica-titaniasupport, wherein said support comprises from about 1 to about 10 weightpercent titanium, based on the weight on the support, wherein saidcatalyst system has a pore volume within a range of about 0.5 to about1.3 ml/g, a surface area within a range about 150 to 400 m²/g, and saidcatalyst system has been activated at a temperature within a range ofabout 800° F. to about 1300° F. (about 427° C. to about 704° C.);

d) a trialkylboron compound; and

e) recovering an ethylene/mono-1-olefin copolymer.

In accordance with another embodiment of this invention, a copolymercomprising ethylene and a mono-1-olefin having from about 3 to about 8carbon atoms carbon atoms per molecule is provided, wherein saidcopolymer has a high load melt index (HLMI) within a range of about 10to about 80 g/10 minutes, a density within a range of about 0.95 to 0.96g/cc, a weight swell lower than about 380%, and a die swell lower thanabout 43%. An environmental stress crack resistance (ESCR) of greaterthan about 200 hours, a M_(w)/M_(n) of greater than about 12 and theonset of melt fracture of greater than about 2000 sec⁻¹.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Catalyst

As used in the description herein, the terms “cogel” and “cogelhydrogel” are arbitrarily used to describe cogelled silica and titania.The term “tergel” is used to describe the product resulting fromgelation together of silica, titania, and chromia. References to“silica” mean a silica-containing material generally comprised of 80 to100 weight percent silica, the remainder, if any, being selected fromalumina, boria, magnesia, thoria, zirconia, or mixtures thereof. Otheringredients which do not adversely affect the catalyst or which arepresent to produce some unrelated results also can be present.

The support for the catalyst of this invention must be a cogel of silicaand a titanium compound. Such a cogel hydrogel can be produced bycontacting an alkali metal silicate such as sodium silicate with such asan acid, carbon dioxide, or an acidic salt. The preferred procedure isto utilize sodium silicate and an acid such as sulfric acid,hydrochloric acid, or acetic acid, with sulfuric acid being the mostpreferred due to less corrosivity and greater acid strength. Thetitanium component must be coprecipitated with silica and thus mostconveniently the titanium compound will be dissolved in the acid oralkali metal silicate solution.

The titanium compound preferably is incorporated with the acid. Thetitanium compound can be incorporated in the acid in any form in whichit will be subsequently incorporated in the silica gel formed oncombination of the silicate and the acid (preferably by means of addingthe silicate to the acid) and from which form it is subsequentlyconvertible to titanium oxide on calcination. Suitable titaniumcompounds include, but are not limited to, halides such as TiCl₃ andTiCl₄, nitrates, sulfates, oxalates and alkyl titanates. In instanceswhere carbon dioxide is used, the titanium, of course, must beincorporated into the alkali metal silicate itself. Also with acidicsalts it is preferred to it) incorporate the titanium compound in thealkali metal silicate and in such instances, preferred titaniumcompounds are water soluble materials which do not precipitate thesilicate, i.e. are those convertible to titanium oxide on calcinationsuch as, for example, K₂TiO(C₂O₄)₂H₂O (titanium potassium oxalate);(NH₄)₂TiO(C₂O₄)₂H₂O and Ti₂(C₂O₄)₃H₂O.

The titanium compound preferably is present in an amount within therange of about 1 to about 10, preferably about 1 to about 8, and mostpreferably about 2 to about 8 weight percent, calculated as titanium,based on the weight of the cogel. The preferred titanium ranges resultin a catalyst system that can have improved activity and a higher meltindex polymer.

The catalyst of this invention must contain a chromium compound. Thechromium compound can be incorporated in any of several separate ways.First, a tergel can be prepared wherein the chromium compound, as wellas a titanium compound, is dissolved in the acidic material or thesilicate and thus coprecipitated with the silica. A suitablechromium-containing compound for use in this embodiment, for example, ischromic sulfate.

Another method to incorporate a chromium compound into the catalyst, isto use a hydrocarbon solution of a chromium compound convertible tochromium oxide to impregnate the support after it is spray dried orazeotrope dried (i.e., the xerogel). Exemplary of such materials aretert-butyl chromate, chromium acetylacetonate, and the like. Suitablesolvents include, but are not limited to, pentane, hexane, benzene, andthe like. Surprisingly, an aqueous solution of a chromium compoundsimply can be physically mixed with the support.

The catalyst system used in the invention must be aged twice, first at asubstantially neutral pH and second at an alkaline pH. This twice-agedprocess is disclosed in U.S. Pat. No. 4,981,831, herein incorporated byreference.

Chromium preferably is present in an amount within a range of about 0.8to about 3 weight percent, more preferably within a range of about 1.5to about 2.5 weight percent chromium calculated as CrO₃, based on thetotal weight of the catalyst (support plus chromium compound). Theseranges of chromium content provide a catalyst system that is execellentin activity.

Optionally a pore perserving agent can be added during catalyst systempreparation, as disclosed in U.S. Pat. No. 4,981,831, hereinincorporated by reference.

The resulting twice-aged catalyst system can be dried in any mannerknown in the art, such as oven drying, spray drying, azeotrope drying,or any other method.

The dried catalyst system then must be calcined. Calcination can takeplace by heating the dried catalyst system in the presence of an excessof molecular oxygen at a temperature within a range of about 800° F. toabout 1300° F. (about 427° C. to about 704° C.), preferably about 900°F. to 1200OF (about 482° C. to about 649° C.). Most preferably, thecatalyst system calcined at a temperature within a range of about 1100°F. to about 1200° F. (about 593° C. to about 649° C.) for about 30minutes to about 50 hours, more preferably for about 2 to about 10hours. This calcination procedure results in at least a substanialportion of the chromium in a low valence state to be converted to ahexavalent form. Preferably, this calcination is carried out in a streamof fluidizing air wherein the stream of fluidizing air is contained asthe material is cooled.

In order to achieve the desired resultant effects on the resin product,or polymer, the catalyst system must have a low pore volume, usuallyabout 0.5 ml/g to about 1.3 ml/g, preferably about 0.8 ml/g to about 1.2ml/g. Additionally, the catalyst system must have a low surface area,usually within a range of about 150 m²/g to about 400 m²/g, preferablywithin a range of about 200 m²/g to 380 m²/g. Most preferably thecatalyst system surface area is within the range of 250 m²/g to 350m²/g.

Catalyst systems of this invention must be used with a cocatalyst. Thecocatalyst must be a trialkylboron compound wherein each alkyl group hasfrom about 1 to about 10 carbon atoms, preferably about 2 to about 4carbon atoms per group. Trialkylboron compounds must be used as acocatalyst because the compounds are effective agents to improve polymerproperties, such as, for example to decrease die swell and to decreaseweight swell. By far, the most preferred cocatlyst is triethylboron.

The cocatalyst is used in an amount within a range of about 1 to about 6parts per million (ppm), or milligram per kilogram (mg/kg), based on theamount of diluent in the reactor. Preferably the cocatalyst is used inan amount within a range of about 2 to about 4 ppm, for costeffectiveness, best polymer properties, and decreasing the amount ofsmoke resulting from the resin during processing.

Reactants

Catalyst systems of this invention can be used to polymerize at leastone mono-1-olefin containing about 2 to about 8 carbon atoms permolecule, preferably ethylene, propylene, 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene, and 1-octene. The invention is of particularapplicability in producing ethylene homopolymers and copolymers frommixtures of ethylene and about 0.5 to about 20 mole percent of one ormore comonomers selected from the group consisting of alpha-olefinscontaining about 3 to about 8 carbon atoms per molecule. Exemplarycomonomers include aliphatic 1-olefins, such as propylene, 1-butene,1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and other olefins andconjugated or non-conjugated diolefins such as 1,3-butadiene,1,4-pentadiene, 1,5-hexadiene, and other such diolefins and mixturesthereof. Ethylene copolymers preferably constitute at least about 90,preferably 97 to 99.8 mole percent polymerized ethylene units. Withethylene/1-hexene copolymers, about 98 to 99.8 mole percent ethylene ispreferred, the remainder of course being comonomer. Propylene, 1-butene,1-pentene, 1-hexene and 1-octene are especially preferred comonomers foruse with ethylene.

Polymerization

Catalyst systems of this invention must used in slurry polymerizationprocesses. A slurry, or particle form, process generally is carried outin an inert diluent (medium). The diluent useful in the practice of thisinvention must be isobutane. While other diluents are known, or even canbe used, other diluents will not result in the decreased die swell anddecreased weight swell as disclosed in this invention.

The temperature of the slurry reactor must be within a range of 200° F.to 225° F. (93° C. to 107° C.). Temperatures outside of that range willnot result in a polymer having the required resultant properties.Pressures in the particle form process can vary from about 110 to about700 psi (0.76 to 4.8 MPa) or higher.

The catalyst system is kept in suspension and is contacted with themonomer(s) at sufficient pressure to maintain the isobutane and at leasta portion of the monomer(s) in a liquid phase. The isobutane andtemperature thus are selected such that the polymer is produced as solidparticles and is recovered in that form. Catalyst system concentrationscan be such that the catalyst content ranges from about 0.001 to about 1weight percent, based on the weight of the reactor contents.

Hydrogen can be added to the slurry polymerization to control molecularweight, as is known in the prior art. When used, hydrogen generally isused at concentrations up to about 2 mole percent of the reactionmixture, preferably within a range of about 0.1 to about 1 mole percentof reaction mixture.

Product

Polymers produced in accordance with this invention must be a copolymerof ethylene and at least one higher alpha-olefin. The comonomer, orhigher alpha-olefin, is present in the polymerization reactor in anamount within a range of about 0 to about 1.0 mole percent.

Copolymers produced according to this invention have a reduced die swelland a reduced weight swell as compared to conventionally preparedpolyethylene copolymer resins. The polymer, or resin product, generallyhas a density within a range of about 0.95 to about 0.96 g/cc,preferably within a range of about 0.952 to about 0.958 g/cc. Mostpreferably polymer product density is within a range of 0.954 to 0.956g/cc. The HLMI of the resultant polymer generally is within a range ofabout 10 to about 80 g/10 minutes, preferably about 13 to about 40 g/10minutes. Most preferably, the HLMI is within a range of 15 to 30 g/IOminutes. The sheer response, or HLMI/MI ratio, is within a range ofabout 100 to about 250, preferably within a range of about 110 to about200. Most preferably, the HLMI/MI ratio is within a range of 125 to 175.

Polymers produced in accordance with this invention also have a broadmolecular weight distribution, as evidenced by the ratio of M_(w)/M_(n).Usually, M_(w)/M_(n), wherein M_(w) is the weight average molecularweight and M_(n) is the number average molecular weight, is within arange of about 10 to about 30, preferably within a range of about 12 toabout 25. Most preferably, the M_(w)/M_(n) is within a range of 15 to22.

The ESCR of products produced from this resin is greater than about 200hours, preferably greater than about 500 hours based on testing underCondition A. Most preferably, the ESCR is within a range of about 1000hours to about 10,000 hours. Further, the resin exhibits low weightswell, which is lower than typical standard blow molding resin such asPhillips Marlex® polyethylene HHM 5502 or Phillips Marlex® polyethyleneHHM 5202 under Uniloy blow molding conditions. Further, resins producedin accordance with this invention, have a low die swell, which is atleast lower than typical standard blow molding resin such as PhillipsMarlex® HM 5502 or Phillips Marlex® HHM 5202 under Uniloy blow moldingconditions.

The normalized die swell of polymers produced in accordance with thisinvention usually is less than about 0.95, preferably less than 0.90.Most preferably, the normalized die swell of polymers produced inaccordance with this invention is less than 0.85 for best polymerprocess throughput.

The onset of melt fracture for polymers produced in accordance with thisinvention is greater than about 2000 sec⁻¹, preferably greater than 2200sec⁻¹. Most preferably, the onset of melt fracture for polymers producedin accordance with this invention is greater than 2300 sec⁻¹ for bestpolymer processing throughput.

Another way to distinguish polymer products produced from this resin isto compare them to currently commercially available ethylene polymers.For example, relative to a Phillips Petroleum MARLEX® 5502 polyethyleneresin, polymers of the present invention generally have a HLMI less than90% of the typical values for MARLEX® 5502, a HLMI/MI ratio of greaterthan 110% of the standard values for MARLEX® 5502, a M_(w)/M_(n) ofgreater than about 110% of typical values for MARLEX® 5502.Additionally, die swell and weight swell of the resins produced inaccordance with the present invention are lower than typical values for5502. The normalized die swell of the inventive resin is generally lessthan 95% of the normalized typical die swell values for MARLEX® 5502 andthe weight swell of the inventive resin is less than about 90% ofstandard or typical values for MARLEX® 5502. However, density of theinventive resin is within the standard ranges of 5502. In addition, theESCR of the inventive resin is more than two times typical ESCR valuesfor 5502.

The following examples are provided to further assist a person skilledin the art with understanding the invention. The particular reactants,conditions, and other variables are intended to be generallyillustrative of these inventions and are not meant to be construed to beunduly limiting the reasonable scope of the invention.

EXAMPLES

Ethylene and higher alpha-olefin copolymers were prepared under 10l)continuous particle form process conditions, comprising contactingcatalyst system with monomers, employing a liquid full, 15.2 cmdiameter, loop reactor, having a volume of 23 gallons (87 liters),isobutane as the diluent, and occasionally some hydrogen, as shown inthe following Examples.

Ethylene that had been dried over alumina was used as the monomer.Isobutane that had been degassed by fractionation and dried over aluminawas used as the diluent. Triethylboron or triethylaluminun was alsosometimes used as a cocatalyst as indicated in the tables below.

The catalyst used for the production of the inventive resins was a lowporosity Cr/silica-titania commercially available from W.R. GraceCompany as 965 Sylopore. It contained 2.5, 3.5, or 5.0 weight percenttitanium as indicated and originally 1.0 weight percent chromium. Insome cases, however, extra chromium was added through impregnation of a0.5% methanol solution of chromium nitrate, as indicated in the tables.Sylopore has a pore volume of about 1.0 cc/g and a surface area ofusually about 350 m2/g. Specific measurements may be shown in the tablesthat follow.

Control resins were made from three other types of commercial catalystsfrom W.R. Grace. The catalyst 969MS (sometimes also referred to as 1%Cron Grade 952 silica) has a pore volume of about 1.6 cc/g and a surfacearea around 300 m2/g. Other control resins were made from 963 and 964Magnapore which contained 1.0 weight percent chromium on a high porositysilica-titania containing either 2.5 or 5.0 weight percent titanium, asindicated. This catalyst had a pore volume around 2.4 cc/g and a surfacearea around 520 m2/g. Still other control resins were made by a catalystdescribed as Cr on HPVSA silica. This silica was also made by W.R. Graceand had a surface area of about 580 m2/g and a pore volume of about 2.2cc/g. The reactor was operated to have a residence time of 1.25 hrs. Tocontrol polymer molecular weight and swelling, the reactor temperaturewas varied over the range of 200° F. to 226° F. (93° C. to 108° C.),depending on the reaction run, unless shown differently, and thepressure was 3.7 MPa (530 psi). At steady state conditions, theisobutane feed rate was 54 lbs/hr, the ethylene feed rate was about 24lbs/hr, and the 1-hexene comonomer feed rate was varied to control thedensity of the product polymer.

Polymer was removed from the reactor at the rate of about 22 lbs perhour and recovered in a flash chamber. A Vulcan dryer was used to drythe polymer under nitrogen at about 60-80 degrees C. Polymer wasrecovered from each run and tested according to the procedures describedbelow.

Polymer resins obtained by this invention are useful for blow moldingapplications. In these examples blow molding evaluations were conductedby blowing a one gallon (105.0+0.5 gm) bottle on a Uniloy 2016 singlehead blow molding machine using a 2.5 inch diameter die, 20 degreediverging die, 32% accumulator position, 8.5 second blow time, 0.10second blow delay, 0.75 second pre-blow delay and a 45 degree F moldtemperature. A reciprocating screw speed of 45 rpm was used, providingparison extrusion at shear rates greater than 10,000/sec through thedie.

Density (g/ml): ASTM D 1505-68 and ASTM D 1928, Condition C. Determinedon a compression molded sample, cooled at about 15° C. per minute, andconditioned at room temperature for about 40 hours.

High Load Melt Index (HLMI)(g/10 min): ASTM D1238, condition E.Determined at 190° C. with a 21,600 gram weight.

Molecular Weight Distribution M_(w)/M_(n): Molecular weights andmolecular weight distributions were obtained using a Waters 150 CV gelpermeation chromatograph with trichlorobenzene (TCB) as the solvent,with a flow rate of 1 mL/minute at a temperature of 140° C. BHT(2,6-di-tert-butyl-4-methylphenol) at a concentration of 1.0 g/L wasused as a stabilizer in the TCB. An injection volume of 220AL was usedwith a nominal polymer concentration of 0.3 g/l (at room temperature).Dissolution of the sample in stabilized TCB was carried out by heatingat 160-170° C. for 20 hours with occasional, gentle agitation. Thecolumn was two Waters HT-6E columns (7.8×300 mm). The columns werecalibrated with a broad linear polyethylene standard (Phillips Marlex®BHB 5003) for which the molecular weight had been determined.

Surface Area and Pore Volume: A “Quantachrome Autosorb-6 Nitrogen PoreSize Distribution Instrument” was used to determined the surface areaand pore volume of the supports. This instrument was acquired from theQuantachrome Corporation, Syosset, N.Y.

Weight Swell (%): Percent weight swell measures the amount the moltenresin expands immediately as it exits the die. It is a measure of the“memory” of the polymer chains as they seek to relax and thus reform thepolymer shape. Weight swell is an important parameter as it determineshow tight the die gap must be adjusted to provide a constant bottleweight. If a resin has high weight swell, the die gap required will betighter to make the proper part weight. In so doing, it will requirehigher stress to push the resin through the die than a lower weightswell resin. Weight swell is defined as the ratio of the die gap to thefinal bottle wall thickness.

Diameter (Die) Swell: Another measurement of swell is die swell ordiameter swell. This is the ratio of the parison diameter to the diediameter. Another way of expressing die swell is to reference thisnumber to the standard commercial blow molding polyethylene resin,MARLEX 5502, obtained from Phillips Petroleum Company. This value,called the normalized die swell, is obtained by dividing the die swellof the resin by the die swell of MARLEX 5502 measured on the sameoccasion, on the same machine, and under the same machine conditions.

Bottle Stress Crack Resistance (hrs): Bottle stress crack resistance wastested using ten 105 gram one gallon bottles made as described about ona Uniloy 2016 machine. The bottles were filled with a 10% Orvus-Kdetergent solution, capped, and placed in a 140 degree F hot room.Bottle failures were noted each day, and a 50% mean failure time wascalculated for each set.

Onset Of Melt Fracture (sec⁻¹): Extruder-capillary die melt fractureresults were obtained using a 1 inch Killion single screw extruder(KL-100) fitted with a barrier screw. Capillary dies were attached tothe end of the extruder with an adaptor. The adaptor was fitted with aDynisco pressure transducer (model TPT432A) with a measurement range of0-5000 psi, which was located just upstream of the entry to thecapillary die. A two-piece capillary die was used. The first sectionconsisted of a detachable orifice (entry angle 90 degrees and zero landlength) with an entry diameter of 1 inch and a exit diameter of 0.15inches. The second section consisted of a capillary with a 0.150 inchdiameter and 2.25 inch land length (L/D=15).

A typical experiment would consist of extruding a polymer over a rangeof low rates (screw RPM) using extruder, adapter, and die temperaturesetting of 170 C. Using the capillary die (described earlier) fitted tothe orifice die, the pressure in the adapter, flow rate at various RPMwere noted along with the RPM at which the onset of melt fractureoccurred. Pressure drop versus flow rate data was also collected usingthe orifice die alone. Using standard calculations for flow throughcapillary dies, this data was then converted to true shear stress versusshear rate for each resin examined.

Example 1

The Table I below shows the characteristics of two resins, wherein Run101 is considered an optimum of the present invention, and Run 102 isconsidered a resin typical of commercial blow molding resins such asPhillips Marlex® HHM 5502. Both Runs were made under similar conditionsand analyzed.

Notice, under the “Blow Molding Data” section of Table I that both theweight swell and the die swell of Run 101 are considerably lower thanfor Run 102. Actually, Run 102 already is considered to be a low dieswell resin compared to many existing resins or catalyst systemsavailable. Notice that Run 101 was processed at a larger die gap thanRun 102, which is indicative of its lower weight swell. The wider diegap thus permitted Run 101 to be processed with less head pressure andat a considerably lower shear rate (about 10,000 vs. 20,000). Thesecharacteristics justify the label of “easy processing resin.”

Notice also under the “Resin Data” section of Table I that the aboveadvantages were accomplished at a higher, not lower, molecular weight,as indicated by the M_(w) data and the HLMI values. Thus, Run 101 couldbe made still more easy to process by lowering the molecular weight tobe closer to that of Run 102. Of course, die swell would increase, butsince the die swell of Run 101 is already lower than Run 102, this couldbe done.

The reason the invention resin could be easily processed, even at highermolecular weight, is due in part to its broader M_(w) data distribution,as evidenced by the M_(w)/M_(n) and the HLMI/MI. Both these values areconsiderably higher for Run 101 than for Run 102, indicating greaterease of flow. The higher HLMI/MI of Run 101 also indicates higher meltstrength, which is needed if the molecular weight is to be decreasedbeyond the Run 102 value. Melt strength is the property that allows theparison to resist sagging from its own weight before being blown into abottle.

Activation energy, Ea, is an indication of the degree of long chainbranching of the resin. In general, a high Ea imparts lower weight anddie swells and also gives the resin more melt strength. Notice that Run101 displays a higher Ea then Run 102.

Notice also in Table I that Run 101 boasts generally equal or betterphysical properties than Run 102, as evidenced by the ESCR-A, ESCRmodified B, bottle ESCR and bottle impact data. All this wasaccomplished at a slightly higher density than Run 102, which wouldnormally penalize these properties.

Another characteristic of Run 101 is the tendency to melt fracture, orripple, giving a rough surface on the bottle. “Melt Fracture Onset” datain Table I is a measure of the maximum shear rate that the resin cantake before it begins to melt fracture. Notice that Run 101 generallycan tolerate equal or higher shear rates than Run 102, and that this isdone at lower die pressure. However, because Run 101 has a lower weightswell, which permits a wider die gap, there is usually no need toprocess the resins at the same shear rates. Run 101 enjoys theadvantage.

“Production Data” in Table I shows that Run 101 also enjoys otheradvantages. The productivity of the catalyst system used for Run 101 isconsiderably higher than Run 102 catalyst system, despite the slightlylower ethylene concentration, and the much lower activation temperature,both of which normally penalize productivity.

Finally, “Subjective Blow Molding Observations” rated various aspects ofthe operations on a subjective 1 to 5 scale wherein 1 is a good ratingand 5 is a poor rating, as observed by the blow molding operator. Theseratings are purely judgmental by the operator, but they are doneblindly, without bias. Run 101 generally processes similar results toRun 102 in these tests, as shown by the ratings in Example I and II. Theone negative observation in Example I, odor, was not confirmed insubsequent tests in Example II, and can thus be dismissed as an anomaly.

TABLE I Run 101 102 Production Data Catalyst Type 2% Cr Sylopore 1%Cr/952 Silica Titanium, wt % 3.5 0 Surface Area, m²/g 320 280 PoreVolume, ml/g 1.03 1.50 Activation Temperature, ° F. 1100 1450 CocatalystTEB None Cocatalyst Concentration, ppm 2.0 0.0 Productivity g pol/gcat/hr 4000 2174 Reactor Temp, ° F. 216 214 Ethylene, mol % 8.43 9.45Resin Data HLMI, g/10 mins 19.40 30.02 HLMI/MI 216 100 Density, g/cc0.9552 0.9533 M_(w) (x 10⁻³) 226.1 165.9 M_(n) (x 10⁻³) 9.37 19.80 Mw/Mn24.10 8.36 Ea, kJ/mol 37.91 33.89 ESCR-A, hours 283 115 ESCR-modified B,hours 115 115 Melt Fracture Onset Shear Rate, sec⁻¹ 2360 1929 DiePressure, psi 1390 1500 Blow Molding Data Weight Swell, % 290 399 DieSwell, % 34.5 42.9 Head Press., psi 4800 5460 Shear Rate, sec⁻¹ 999319683 Die Gap, inches 0.0208 0.0168 Subjective Blow Molding Observations1 to 5 (1 = good, 5 = poor) Smoke 3 3 Surface 3 2 Ease of Processing 3 2Odor 5 3 Bottle Properties ESCR, hours <700 372 Dart Impact, ft 11.5 <12

Example 2

Table II lists another series of runs, this time made with less TEB 20in the reactor and less chromium on the catalyst system. The samecharacteristics that distinguished Run 101 in Example I also are evidenthere. Notice that invention Runs 201 and 202 exhibit considerably lowerdie and weight swells, and that they could be processed at generallywider die gaps in this Example. This in turn permits Runs 201 and 202 tobe processed at much lower shear rates. Again this indicates an “easyprocessing resin” despite the generally higher molecular weight of Runs201 and 202.

Notice also in Example II that Runs 201 and 202 begin to melt fractureat about the same point as Runs 203-207, which because of the wider diegap, gives Runs 201 and Run 202 a considerably advantage in processing.

Notice also that the bottle properties (ESCR) of Runs 201 and 202 areconsiderably improved over control Runs 203-207.

The productivity of the catalyst system in invention Runs 201 and 202 ismuch better than control Runs 203-207, despite the lower activationtemperature.

The breadth of the molecular weight distribution is increased in Runs201 and 202, as determined by M_(w)/M_(n) values, and the shear response(HLMI/MI) also is increased which indicates the superior melt strengthof Runs 201 and 202. Ea also is higher, indicating a higher level oflong chain branching for Runs 201 and 202. Other process ratings areroughly equivalent for all Runs.

TABLE II Run 201 202 203 204 205 206 207 Production Data Catalyst Type BA A A A A A Activation Temperature, ° F. 1450 1450 1100 1100 1100 11001100 Cocatalyst None None TEB TEB TEB TEB TEB Cocatalyst Concentration,ppm 0 0 1 1 1 1 1 Productivity, g pol/g cat/hr 1887 2222 5000 5556 50004167 4545 Reactor Temperature, ° F. 217 218 211 213 214 216 218Ethylene, mol % 10.03 13.83 10.30 9.90 9.50 9.10 10.00 Resin Data HLMI,g/10 mins 37.56 31.53 19.8 11.07 12.76 12.46 11.5 HLMI/MI 92 102 141 185182 178 230 Density, g/cc 0.954 0.9551 0.9512 0.9532 0.9545 0.953 0.954M_(w) (× 10⁻³) 158.18 128.71 203.90 189.61 236.59 174.86 210.04 M_(n) (×10⁻³) 15.28 16.30 8.60 9.70 11.0 10.10 9.10 M_(w)/M_(n) 10.35 7.86 23.4719.44 21.49 17.15 23.01 Ea, kJ/mol 34.15 33.95 34.11 35.89 35.39 36.6936.21 ESCR, hours 42 64 >1000 >1000 594 726 428 ESCR - modified B, hours<24 <24 411 127 104 87 87 Onset of Melt Fracture Shear Rate, sec⁻¹ 24372418 2348 2298 2313 2350 2227 Die Pressure, psi 1460 1590 1390 1480 14901540 1500 Blow Molding Data Weight Swell, % 445 405 368 321 328 327 313Die Swell, % 44.6 46.7 42.3 36.7 37.3 36.5 39 Head Press., psi 5290 54105080 5350 5510 5490 5650 Shear Rate, sec⁻¹ 26145 21736 13278 12063 1474913928 13565 Die Gap, inches 0.0153 0.0168 0.0173 0.0196 0.0190 0.01900.0199 Cycle Time, sec 15.7 15.7 24.5 15.3 14.9 15.2 15.0 SubjectiveBlow Molding Observations 1 to 5 (1 = good, 5 = poor) Smoke 2 2 3 3 3 33 Surface 3 2 3 3 3 3 3 Ease of Processing 2 2 3 2 2 2 2 Odor 3 2 2 2 22 2 Bottle Properties ESCR, hours 134 569 Dart Impact, ft 7.2 4.6Catalyst: A is 1% Cr on Grade 952 Silica; (Surface area = 280 m²/g; porevolume = 1.5 cc/g, 0% Ti) B is 1% Cr on Sylopore silica-titania (Surfacearea = 340 m²/g; pore volume = 1.0 cc/g, 3.5 wt % Ti)

Example 3

Table III in Example III lists three resins which demonstrate theimportance of the pore volume and surface area of the catalyst system.These resins were made at similar reactor conditions, with the samelevel of cocatalyst, at the same activation temperature, with the samelevel of titania, and at similar HLMI and density. Only the surface areaand pore volume of the silica-titania catalyst system were different;they were considerably higher. Because of the difference, the die swelland weight swell of the resins were much higher and thus do not qualifyas “easy processing resins.” This happened even though the catalystsystem contained higher levels of chromium than ordinary, in an attemptto minimize both weight and die swell.

This example also shows the effect of substituting triethylaluminum(TEA) as cocatalyst in place of TEB. Notice that the molecular weightdistribution is narrowed, as indicated by M_(w)/M_(n) and by HLMI/MI.Die swell also increased slightly, catalyst productivity decreased, theonset of melt fracture declined to much lower shear rates, and the ESCRis severely penalized.

Example III teaches that although increasing the chromium level on thecatalyst seemed to help the swell for the invention resins, it does notimprove weight swell or die swell of resins made with high porositycatalysts.

TABLE III Run 301 302 303 Production Data Catalyst Type 2% Cr 2% Cr 1%Cr Magnapore Magnapore Magnapore-HT Ti, wt % 2.5 2.5 5.0 SurfaceArea,m²/g 550 550 550 Pore Volume, ml/g 2.42 2.42 2.26 ActivationTemperature, 1100 1100 1000 ° F. Cocatalyst TEA TEB TEB CocatalystConcentration, 2.0 2.0 2.0 ppm Productivity, g pol/g cat/hr 4167 58823226 Reactor Temperature, ° F. 219 208 210 Ethylene, mol % 7.8 10.0 7.4Resin Data HLMI, g/10 mins 17 17.2 28.7 HLMI/MI 113.3 191 168.8 Density,g/cc 0.9533 0.9559 0.9562 M_(w) (x 10⁻³) 263 184.3 234.1 M_(n) (x 10⁻³)10.9 8.6 7.26 Mw/Mn 24 21.4 32.2 Ea, kJ/mol 33.76 35 34.3 ESCR-A, hours400 >1000 >1000 ESCR-modified B, hours 85 144 233 Onset of Melt FractureShear Rate, sec⁻¹ 1031 2234 2293 Die Pressure, psi 1330 1420 1290 BlowMolding Data Weight Swell, % 325 414 399 Die Swell, % 45.1 44.9 43.9Head Press, psi 5500 5790 5470 Shear Rate, sec⁻¹ 15654 20771 20595 DieGap, inches 0.0195 0.0162 0.0157 Cycle Time, sec 15.3 14.9 — SubjectiveBlow Molding Observations 1 to 5 (1 = good, 5 = poor) Smoke 2 3 3Surface 2 2 2 Ease of Processing 2 3 4 Odor 2 3 4 Bottle PropertiesESCR, hours >700 >700 287 Dart Impact, ft 75 4.0 11.0

Example 4

This example shows the effect of using a silica catalyst in place of theprescribed silica-titania catalyst. Otherwise, all the other prescribedproduction conditions are met by these runs. A TEB cocatalyst is usedalong with low activation temperature, and even higher chromium in Run401.

Run 401 was made with a high porosity silica-supported catalyst,displaying high pore volume and high surface area. Run 401 exhibits highweight swell and high die swell. Thus, Run 401 does not qualify as aneasy processing resin.

Run 402 was made with a lower porosity silica-supported catalyst systemcontaining no titanium. This time both die swell and weight swell showedimprovement, although not to the same degree Runs 101, 201, and 202.However, the breadth of the M_(w)/M_(n) distribution was not as broad aswhen the catalyst was a silica-titania support instead of a silicasupport. Most importantly, however, was a decline in ESCR compared toRuns 101, 201, and 202. Thus, Runs 401 and 402, do not qualify in everyrespect to the requirements of an easy processing resin.

TABLE IV Run 401 402 Production Data Catalyst Type 2% Cr on 1% Cr onHPVSA Silica Grade 952 Silica Surface Area, m²/g 577 300 Pore Volume,ml/g 2.21 1.50 Activation Temperature, 1000 1200 ° F. Cocatalyst TEB TEBCocatalyst Concentration, 2.0 2.0 ppm Productivity, g pol/g cat/hr 76925556 Reactor Temperature, ° F. 218 220 Ethylene, mol % 9.8 6.7 ResinData HLMI, g/10 mins 20.7 13.6 HLMI/MI 138 227 Density, g/cc 0.95390.9546 M_(w) (x 10⁻³) 202 2073 M_(n) (x 10⁻³) 11.5 14.3 Mw/Mn 17.5 14.4Ea, kJ/mol 34.4 37.71 ESCR-A, hours 395 234 BSCR-modified B, hours 90 44Onset of Melt Fracture Shear Rate, sec⁻¹ 2455 2268 Die Pressure, psi ? ?Blow Molding Data Weight Swell, % 401 314 Die Swell, % 42.3 38.0 HeadPress, psi 3350 5410 Shear Rate,sec⁻¹ 18604 13572 Die Gap, inches 0.01670.0208 Cycle Time, sec 15.4 15.3 Subjective Blow Molding Observations 1to 5 (1 = good, 5 = poor) Smoke 2 2 Surface 3 2 Ease of Processing 2 2Odor 2 2 Bottle Properties ESCR, hours nt 443 Dart Impact, ft nt 3.4

Examples 5 and 6

Finally, Runs in Examples V and VI show the necessity of using a lowactivation temperature, and also of using TEB cocatalyst. In Example Vthe catalyst systems had the correct silica-titania composition and thecorrect porosity, but they were activated at temperatures higher than inaccordance with this invention. The catalyst support used in Run 501 was5 wt % titania and the support used in Run 502 was 2 wt % titania.Notice that ESCR was not much improved over the standard blow moldingresin, shown in Run 503. This also is evident in Example VI which showsa series of Runs made with the inventive catalyst system but activatedat temperatures ranging from 1100° F. up to 1400° F. Notice the strongdependence of ESCR on activation temperature. As prescribed, 1100° F.appears to be far preferable to other activation/calcinationtemperatures.

These two examples also show the effect of leaving out cocatalyst. Inall Runs the right catalyst system was used, but no TEB was added to thereactor. Notice that the die swell, as measured this time in Example Vby layflat, is not improved over the standard resin, Run 102. Example VIlists the calculated die swell. Notice that at the preferred 1100° F.activation temperature, the die swell is actually much worse than thestandard blow molding resin, Run 605. Notice also that in both examplesnone of the resins exhibit sufficiently high melt strength, as indicatedby HLMI/MI, and that ESCR does not really equal that of the inventionRuns. Thus, the TEB cocatalyst is considered to be an essential part ofthe invention.

TABLE V Run 501 502 503 Catalyst Sylopore Sylopore 969 ms Ti, wt % 5.02.5 0 Activation Temperature, 1300 1500 1400 ° F. TEB, ppm 0 0 0 ReactorTemperature, ° F. 214 213 217 HLMI, g/10 mins 41.4 25.8 35 HLMI/MI 115136 105 Density, g/cc 0.955 0.954 0.955 Productivity, g pol/g 3280 25302500 cat/hr ESCR-A, hours 180 134 100 Bottle ESCR, hours 135 130 100Bottle Impact, ft 8 6 7 Die Swell (Layflat), % 5.44 5.35 5.45 Smoke 1 31 Ease of Processing 1 2 1

TABLE VI Run 601 602 603 604 605 Catalyst Sylopore Sylopore SyloporeSylopore 969 MS Ti, wt % 2.5 2.5 2.5 2.5 0 Activation 1100 1200 13001400 1400 Temperature, ° F. TEB, ppm 0 0 0 0 0 Reactor 228 228 219 226217 Temperature, ° F. HLMI, g/10 38.1 45.3 30.5 41.6 33.4 mins HLMI/MI61.7 70.4 91.5 87 93 Density, g/cc 0.950 0.9581 0.956 0.9615 0.955Productivity, 1613 2174 2381 6250 2500 g pol/ g cat/ hrs ESCR-A, 309 78116 36 85 hours Bottle >700 110 300 76 205 ESCR, hours Bottle >12 11.511.5 6.5 >12 Impact, ft Die Swell, % 50.8 44.0 37.5 41.2 38.0 Die Gap,na 0.025 0.025 0.0214 0.0197 inches (wt swell) Smoke 2 2 2 2 2 Ease of 32 3 2 2 Processing

While this invention has been described in detail for the purpose ofillustration, it is not to be construed or limited thereby. Thisdetailed description is intended to cover all changes and modificationswithin the spirit and scope thereof.

That which is claimed is:
 1. A polymerization process comprisingcontacting under slurry polymerization conditions at a temperaturewithin a range of about 200° F. to about 226° F. (about 93° C. to about108° C.) in an isobutane diluent: a) ethylene monomer; b) at least 1mono-1-olefin comonomer having about three to eight carbon atoms permolecule; c) a catalyst system comprising chromium supported on asilica-titania support, wherein said support comprises from about 1 toabout 10 weight percent titanium, based on the weight on the support,wherein said catalyst system is aged twice and wherein the first agingis at a substantially neutral pH and wherein the second aging is at analkaline pH, said catalyst system has a pore volume within a range ofabout 0.5 to about 1.3 ml/g, a surface area within a range about 150 to400 m²/g, and said catalyst system has been calcined at a temperaturewithin a range of about 800° F. to about 1300° F. (about 427° C. toabout 704° C.); d) about 1 to about 6 mg/kg, based on total reactorcontents, of a trialkylboron compound; and e) recovering anethylene/mono-1-olefin copolymer.
 2. A process according to claim 1wherein said comonomer is selected from the group consisting ofpropylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and mixturesthereof.
 3. A process according to claim 2 wherein said comonomer is1-hexene.
 4. A process according to claim 1 wherein said reactortemperature is within a range of about 210° F. to 220° F.
 5. A processaccording to claim 1 wherein said titania of the silica-titania supportis coprecipitated with the silica.
 6. A process according to claim 1wherein said trialkyboron cocatalyst is present in the reactor in anamount within a range of 2 to about 4 mg/kg.
 7. A polymerization processcomprising contacting under slurry polymerization conditions at atemperature within a range of about 210° F. to about 220° F. in anisobutane diluent: a) ethylene monomer; b) 1-hexene comonomer; c) acatalyst system comprising chromium supported on a silica-titaniasupport, where in said support comprises from 2 to 8 weight percenttitanium, based on the weight on the support, wherein said catalystsystem is aged twice and wherein the first aging is at a substantiallyneutral pH and wherein the second aging is at an alkaline pH, saidcatalyst system has a pore volume within range of 0.8 to 1.2 ml/g, asurface area within a range of 250 to 350 m²/g, and said catalyst systemhas been calcined at a temperature within a range of 1100° F. to 1200°F.; d) about 2 to about 4 mg/kg, based on total reactor contents, of atriethylboron cocatalyst; and e) recovering an ethylene/1-hexenecopolymer.